Melt the butter in a medium saucepan over medium heat and cook, stirring frequently, until the butter froths then you see little brown bits form on the bottom of the pan, 4-5 minutes. Immediately transfer the brown butter to a separate bowl to cool slightly.

While it’s cooling, whisk together the flour, baking soda, and salt in a large bowl.

When the browned butter is slightly cooled, add the brown sugar and granulated sugar to the saucepan and whisk to combine. Whisk in the eggs and vanilla until no yellow streaks remain.

Pour the wet ingredients into the flour mixture and stir with a rubber spatula until combined. It will be dry at first then start to come together.

Add the chopped chocolate and stir to combine. If the butter is too warm and you try to add the chocolate some of the chocolate can melt. Cover the dough and refrigerate to chill for at least 2 hours or up to 3 days.

Line a large baking sheet with parchment paper. Using a heaping teaspoon, scoop the pistachio cream out onto the prepared baking sheet. Transfer to the freezer to chill until the dough is done chilling.

Preheat the oven to 350°F. Line a large baking sheet with parchment paper. If the dough has been chilling for longer than 12 hours, let it sit at room temp for 30 minutes before scooping because it’s easier to handle.

Use a large (1/4 cup) cookie scoop to scoop out the dough. Break the dough ball in half and press an indent into the center of one half. Place the chilled pistachio cream in the center then close the dough ball with the other half, pinching the seams to seal it.

Arrange the cookie dough balls on the prepared baking sheet. Bake in the preheated oven for 10-12 minutes, until the edges are set and the tops are just barely set. Cool on the baking sheet for 10 minutes and press additional chocolate chunks in the tops if desired. Sprinkle with flaky sea salt. Transfer to a wire rack to cool completely.